Yogi: The awareness is weaker when the headache goes away (and the new object is more subtle).
Sayadaw: If your awareness is not strong enough, when the object is obvious the mind is also strong (more energy). If the object is subtle, the mind is also weak (less energy) because the awareness is not strong enough.
If you choose a subtle object, the mind has no energy because awareness is not strong enough. If the object is obvious, then the mind wakes up.